1. Field
The present invention relates generally to the manufacture of semiconductor devices. In particular, the present invention relates to the formation of a single-crystal Group-III Nitride film with a desired orientation on a patterned substrate.
2. Discussion of Related Art
Single-crystal Group III-Nitride films and related optical and electrical devices are typically grown from planar c-plane sapphire substrates, with the (0001)/c-plane of the Group III-Nitride film oriented in the z-direction, normal to the substrate surface. The c-plane of a Group III-Nitride is polar and has a piezoelectric field; both properties can affect device performance due to energy band distortion, separation of electrons and holes, and reduction of the radiative recombination efficiency. In LED devices, c-plane polarization also causes increasing blue-shift in the peak emissions wavelength as the injection current increases.
A-plane and m-plane Group III-Nitride films may also be grown from planar sapphire substrates. Group III-Nitride a- and m-planes are non-polar. However, films grown in the direction of these planes typically have a higher threading dislocation density and basal-plane stacking faults than c-plane Group III-Nitride films. Threading dislocations form due to differences in lattice constant, thermal expansion coefficient (TEC) and interfacial surface energy between the Group III-Nitride film and the sapphire substrate. Threading dislocations can negatively impact device efficiency and performance.
Group III-Nitride films may also be grown from planar silicon substrates. Such films typically have even greater threading dislocation densities when compared to films grown on planar sapphire substrates due to larger differences in lattice constant and TEC between silicon and Group III-Nitrides. Lattice constant and TEC differences also can give rise to high film stress, which, compounded over the surface of the substrate, can lead to wafer-bowing or film delamination. Buffer and transition layers may be used to reduce the impact of lattice constant and TEC differences on Group III-Nitride films and devices.
Growth of Group III-Nitride films from patterned substrates using methods such as epitaxial lateral overgrowth (ELO) or pendeo-lateral epitaxy can produce films with lower threading dislocation densities. Lateral-growth methods reduce threading dislocation density through the dislocation bending phenomena, wherein a change in the direction of film growth terminates existing threading dislocations.